1. Field of the Invention
The invention relates to a viscosity stable aqueous dispersion suitable for coloring water-based cosmetics, paper coatings and inks for food packaging. More particularly, the present invention relates to an aqueous dispersion which contains at least one Food, Drug and Cosmetic ("FD&C") and/or Drug and Cosmetic ("D&C") pigment dispersed in water with a polysaccharide resin.
2. Related Art
Only pigments which have been certified for cosmetics or direct food contact can be used for coloration of water-based cosmetics, food and food packaging such as candy wrappers. Common pigments used in cosmetics include: D&C Red 6 (Disodium Salt), D&C Red 6 (Barium Lake), D&C Red 7 (Calcium Lake), FD&C Yellow 5 (Aluminum Lake), FD&C Yellow 6 (Aluminum Lake), FD&C Yellow 10 (Aluminum Lake) and FD&C Blue I (Aluminum Lake). These above-mentioned pigments are salts of the corresponding FD&C and D&C dyes.
The FD&C dyes and the D&C dyes all have functional sites, such as carboxylic groups or sulfonates, which provide excellent water solubility. However, water solubility can lead to undesirable problems such as dye bleeding and staining. To prevent these problems, FD&C dyes and D&C dyes are made water insoluble by converting ("laking") their functional sites to salts with metal ions, such as sodium, barium, calcium or aluminum.
The formulator is faced with a dilemma because, while it is desirable for the pigments to be water insoluble once applied to the cosmetic or food packaging, it is also important for the pigment to be evenly distributed during printing or coloration of the cosmetic or food packaging. In short, the formulator must be able to evenly disperse the water-insoluble laked FD&C and D&C pigments in water in order to apply them.
Dispersion of these FD&C pigments into water presents a difficult challenge. The laked pigments contain large amounts of metal ions, such as aluminum, barium or calcium, which can cause very large viscosity increases in aqueous systems. For example, aluminum ion forms aluminum hydroxide in water, in which a number of water molecules are "attached" or hydrated to the aluminum ion. Given enough aluminum ions, water can eventually gel completely due to the water of hydration and also to the structuring of the neighboring water molecules via hydrogen bonding.
Alkali-sensitive styrene-acrylic resins are commonly used in printing inks for dispersion of industrial organic pigments (such as phthalocyanine blue, diarylide yellow or carbon black). However, these acrylics are not effective in stabilizing FD&C or D&C pigments in water by themselves, and can aggravate the gellation problem since the aluminum ions can attach themselves to the acrylate functionality, and because styrene acrylic resins become water insoluble at low pH.
U.S. Pat. No. 5,059,248 discloses an aqueous dispersion composition which includes FD&C or D&C pigment and a salt of ethylenediaminetetracetic acid or nitrilo triacetic acid as a stabilizing agent. The dispersion may additionally contain a lower alkanol and/or a water soluble plasticizer. Film-forming resins such as methyl cellulose, hydroxypropylmethyl cellulose, ethyl cellulose, cellulose acetate phthalate, shellac and polyvinyl pyrrolidone may also be included in the aqueous dispersion.
U.S. Pat. No. 4,652,313 discloses aqueous lake pigment suspensions which include FD&C lakes, a polymeric colloid such as gum arabic, guar gum, agar, xantham gum, PG alginate, hydroxypropyl cellulose, and polymeric colloids such as corn starch or polyvinylpyrrolidone may be included in the suspension.
U.S. Pat. No. 5,753,021 discloses pigmented ink jet ink compositions which contain modified polysaccharide resin, a carrier and a pigment. "Universal Pigment Dispersions," a brochure from Lorama Chemicals, Inc., discloses aqueous dispersions containing polysaccharide resin, styrene acrylate and ethylenediaminetetraacetic acid for use in paint compositions.
An object of the present invention is to provide an aqueous pigment dispersion containing FD&C and/or D&C pigments which will uniformly color food packaging, and will not bleed or stain once deposited.